Yo'av,
You didn't send the message to the list, I think - just to me
personally, so Donald and Terry probably didn't see your answer.
In any case I believe there is no Hugin mystery here.
First, as I wrote, if you scan the same photo twice, even with different
resolutions, it should be enough
Terry, I have no idea why you got the odd effects you saw in the example
you attached to your post of Mon, 06 Apr 2015 at 16:27:23 +1000. I did
find at one point that one of my constituent images suddenly vanished
except for one corner. That proved to be because a crop had been
incorporated,